Electron microscopic, freeze-fracture, and experimental studies on the seminiferous epithelium of the mammalian testis will be continued in an effort to understand the factors responsible for establishment and maintenance of the blood-testis permeability barrier. Efforts to dissociate and isolate relatively pure fractions of structural components of the mammalian spermatozoan will be continued. Isolation and chemical characterization of the outer dense fibers has been achieved. Attention will now be directed to isolation of the fibrous sheath. The several cytologically distinct segments of the epididymis will be studied morphologically and by assays for cytoplasmic androgen receptor protein; - after efferent duct ligation, castration, and androgen replacement, in an effort to determine the degree of dependence of the various parts of the duct on intraluminal vs. circulating androgen.